3D and 4D Fetal Ultrasound Advances Spark Research, Create Challenges

May 01, 2013

Advances in 3D and 4D ultrasound technology now offer capabilities ranging from better visualization of congenital birth defects to dynamic, multiplanar views of the fetal heart.

Along with advances on the research front, the growing availability of 3D and 4D ultrasound technology has also increased public access to these ultrasound services—increasing the potential for safety risks to both mothers and their fetuses, expert say.

The mainstream press has been filled with reports of the latest trend for expectant parents—“ultrasound parties,” where a technologist performs ultrasound in the home and 3D and 4D images are immediately shared with friends and family in a celebratory environment. Party attendees view still 3D ultrasound images of the fetus and 4D ultrasound images that appear to show fetal movement in real time.

A host of new independent ultrasound services are helping parents turn what has traditionally been a private medical procedure into what one media outlet has dubbed “a new frontier in pregnancy oversharing.” Experts caution against using ultrasound for entertainment and stress that ultrasound should be performed on expectant mothers only when there is a clear diagnostic benefit.

“Patients, of course, love 3D pictures, but as radiologists we have to be careful that we’re not performing an ultrasound for the fun of it,” said Deborah Levine, M.D., co-chief of ultrasound and director of obstetric and gynecologic ultrasound in the Department of Radiology at Beth Israel Deaconess Medical Center in Boston. “Radiologists will perform a whole diagnostic study before ever providing that 3D picture for the patient.”

As for companies that provide these ultrasound services in parents’ homes, “I want to be clear that as radiologists we don’t condone them,” said Dr. Levine, also a professor of radiology at Harvard Medical School. “They’re strictly for entertainment and don’t serve a diagnostic purpose.”

Such ultrasound services pose a potential safety issue for patients, said Wesley Lee, M.D., co-director of the Texas Children’s Fetal Center at the Texas Pavilion for Women in Houston, who presented “3D Imaging of the Fetus” at RSNA 2012. In general there is minimal risk with ultrasound if used appropriately, Dr. Lee said. “But if it is performed by a person not properly trained who is putting that transducer over the mother for hours and hours, then the question becomes whether it’s safe for the fetus,” added Dr. Lee, also a professor and section chief of women’s and fetal imaging in the Department of OBGYN at Baylor College of Medicine, Houston.

The American Institute of Ultrasound in Medicine (AIUM) states that using ultrasound to view, take a picture of, or find out the gender of a fetus without a medical indication runs contrary to good practice.

AIUM offers resources on using ultrasound for entertainment purposes, including information sheets that ultrasound practices can print and distribute to patients. (See sidebar)

Clinical 3D-4D Ultrasound Have “Mix and Match” Potential

Developed more than 30 years ago, 3D ultrasound technology has been widely used in clinical practice in the last decade and continues to widen its reach as researchers explore innovative new applications.

The technology provides physicians a “nice way to view surface characteristics of the fetus,” Dr. Levine said. “And there are certain anomalies that are easier to understand when you see them in 3D.” For example, 3D imaging can offer physicians a better view of birth defects such as a cleft lip and clubfoot, she said.

Dr. Levine also pointed out the illustrative benefits of 3D ultrasound for patients and physicians. “An ultrasound expert may understand an anomaly in 2D images, but frequently patients and the doctors counseling those patients have an easier time understanding a 3D image,” she said.

“Most of us are classically trained with 2D ultrasound and most of the diagnoses are pretty straightforward,” Dr. Lee said. “But sometimes you come out of an exam scratching your head without being entirely sure about a certain finding. Whether you are talking about 2D, 3D or 4D ultrasound, there are several different imaging modalities you can use depending on what kind of answers you are seeking.”

There are many different tools available in 3D ultrasound, such as the multiplanar display, where physicians are able to see, for example, orthogonal views of the fetal brain and its cavities, simultaneously, Dr. Lee said. “Navigating through these volumes with multiplanar views can be really helpful,” he added.

Surface rendering of 3D ultrasound images allows physicians to view the features of a baby’s face or hands or other surface details that allow them to search for genetic syndromes. Tools like maximum intensity projection let doctors better visualize fetal bony structures such as the skull or vertebra, while 3D inversion mode gives them the ability to examine fluid-filled structures, such as the fetal stomach or brain ventricles that ordinarily appear black in ultrasound. Thick slice scanning provides physicians a better look at fingers and toes, and anomalies like cleft palate.

When it comes to 4D ultrasound, spatial temporal image correlation (STIC) “is an innovative way to examine a moving heart, so that you can actually have dynamic multiplanar views of the heart,” Dr. Lee said. “And you can actually use all of these tools I’ve talked about to render the heart in 4D.”

All of these imaging tools, according to Dr. Lee, can be “mixed and matched. For example, in the case of an obstetric complication like vasa previa, doctors can use 3D ultrasound to obtain a rendered view that can be combined with, for example, color Doppler. “We can mix and match these modalities to see things in different ways that traditional ultrasound can’t show you,” Dr. Lee said.

3D Ultrasound Helps Assess Prenatal Nutritional Status

3D ultrasound also allows physicians to search quantitatively for information, which is driving Dr. Lee’s recent research on improving the precision of estimated fetal weight using fractional thigh volume measurements based on 3D scans.

Obstetricians have long relied on estimated weight to make decisions about the growth and health of a fetus. “Unfortunately, estimated birth weight doesn’t do a terrific job predicting postnatal nutritional status,” Dr. Lee said. Assessing the soft tissue of fetal limbs is a new method of assessing prenatal nutritional status, said Dr. Lee, who has spent several years studying the reliability of fractional fetal limb volume as assessed by 3D ultrasound.

In a prospective study published in the March 2013 issue of Ultrasound in Obstetrics & Gynecology, Dr. Lee and colleagues determined that the precision of a fetal weight estimation model using fractional limb volume (in this case the thigh), abdominal circumference and biparietal diameter was superior to that of the commonly used Hadlock method (based on biparietal diameter, abdominal circumference and femur length).

“We have to develop new ways and novel approaches for determining which babies are truly malnourished,” Dr. Lee said, “That’s why we are using fractional limb volume as part of the fetal weight estimation procedure to assess the fetus before delivery.”